U.S. patent application number 14/525316 was filed with the patent office on 2015-02-12 for laser scanner having a multi-color light source and real-time color receiver.
The applicant listed for this patent is FARO Technologies, Inc.. Invention is credited to Reinhard Becker, Robert E. Bridges.
Application Number | 20150043009 14/525316 |
Document ID | / |
Family ID | 52448411 |
Filed Date | 2015-02-12 |
United States Patent
Application |
20150043009 |
Kind Code |
A1 |
Bridges; Robert E. ; et
al. |
February 12, 2015 |
LASER SCANNER HAVING A MULTI-COLOR LIGHT SOURCE AND REAL-TIME COLOR
RECEIVER
Abstract
A laser scanner includes a light emitter that generates a
modulated light beam for measuring distance and red, blue, and
green lights for capturing colors. The beam is collimated and
directed to an object point with a steering mirror. Reflected light
from the object point is directed by the steering mirror onto
scanner optics. The reflected light is directed to an optical
receiver that sends the first light in a first path and the second,
third and fourth lights in a second path to a color receiver. The
first light is demodulated to determine distance to the target. The
second, third, and fourth lights are separated and measured to
determine three color values. The color values are combined with
the measured distance value to determine a color 3D coordinate for
the object point.
Inventors: |
Bridges; Robert E.; (Kennett
Square, PA) ; Becker; Reinhard; (Ludwigsburg,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FARO Technologies, Inc. |
Lake Mary |
FL |
US |
|
|
Family ID: |
52448411 |
Appl. No.: |
14/525316 |
Filed: |
October 28, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13259446 |
Dec 2, 2011 |
|
|
|
PCT/EP2010/001779 |
Mar 22, 2010 |
|
|
|
14525316 |
|
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|
|
61299566 |
Jan 29, 2010 |
|
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Current U.S.
Class: |
356/610 |
Current CPC
Class: |
G01S 17/36 20130101;
G01S 7/4815 20130101; G01C 15/002 20130101; G01S 17/86 20200101;
G01S 7/4812 20130101; G01S 17/42 20130101; G01S 7/4817 20130101;
G01S 17/89 20130101; G01S 7/4816 20130101 |
Class at
Publication: |
356/610 |
International
Class: |
G01C 15/00 20060101
G01C015/00; G01S 17/89 20060101 G01S017/89; G01S 17/32 20060101
G01S017/32 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2009 |
DE |
10 2009 015 920.7 |
Claims
1. A laser scanner for optically scanning and measuring an
environment, comprising: a light emitter configured to emit an
emission light beam, the emission light beam being a superposition
of a first light, a second light, a third light, and a fourth
light, the first light being modulated, the second, third, and
fourth lights each having a different wavelength in the visible
spectrum; a collimator configured to collimate the emission light
beam; a steering mirror having a reflective surface and configured
to rotate about a first axis, the steering mirror further
configured to deflect the emission light beam onto an object point
in the environment and to receive a reception light beam reflected
from the object point; scanner optics configured to receive the
reception light beam from the steering mirror; an optical receiver
configured to receive the reception light beam from the steering
mirror, the optical receiver further configured to send the first
light in a first path and to send the second, third, and fourth
lights in a second path; a control and evaluation unit configured
to receive the first light in the first path, to convert the first
light into a first electrical signal, and to determine a distance
to the object based at least in part on the first electrical
signal; a color receiver configured to receive the second, third,
and fourth lights on the second path, to convert the second, third,
and fourth lights into second, third, and fourth electrical
signals, and to determine a first color value, a second color
value, and a third color value based at least in part on the
second, third, and fourth electrical signals; a measuring head
configured to rotate around a second axis perpendicular to the
first axis, the first axis and the second axis intersecting in a
gimbal point, the gimbal point being located on the steering
mirror; and a processor configured to determine a three-dimensional
color representation of the object point, the three-dimensional
color representation based at least in part on the distance to the
object, the first color value, the second color value, and the
third color value.
2. The laser scanner of claim 1 further comprising: a first angular
encoder configured to measure a first angle of rotation about the
first axis; and a second angular encoder configured to measure a
second angle of rotation about the second axis.
3. The laser scanner of claim 2 wherein the processor is further
configured to determine a three-dimensional color representation of
the object point based on the first angle of rotation and the
second angle of rotation.
4. The laser scanner of claim 1 wherein the color receiver further
includes a first optical element configured to separate the second,
third, and fourth lights.
5. The laser scanner of claim 4 wherein the first optical element
is configured to direct the second light, third light, and fourth
light to a second optical detector, a third optical detector, and a
fourth optical detector, respectively, to obtain the second
electrical signal, the third electrical signal, and the fourth
electrical signal, respectively.
6. The laser scanner of claim 5 wherein the color receiver further
includes an analog-to-digital converter configured to receive the
second electrical signal, the third electrical signal, and the
fourth electrical signal, and to determine in response the first
color value, the second color value, and the third color value,
respectively.
7. The laser scanner of claim 5 wherein the color receiver further
comprises an optical bandpass filter optically disposed in front of
each one of the second, third, and fourth optical detectors,
respectively.
8. The laser scanner of claim 5 wherein the light emitter includes
a second optical element configured to combine the first, second,
third, and fourth lights, the second optical element including a
plurality of dichroic beam splitters.
9. The laser scanner of claim 5 wherein the second, third, and
fourth lights are modulated at a second, third, and fourth
frequency respectively, the second, third, and fourth frequencies
each being a different frequency.
10. The laser scanner of claim 9 wherein the second electrical
signal, the third electrical signal, and the fourth electrical
signal are sent through a first bandpass filter, a second bandpass
filter, and a third bandpass filter, respectively, each of the
first bandpass filter, the second bandpass filter, and the third
bandpass filter having a different center frequency.
11. The laser scanner of claim 1 wherein the processor is further
configured to determine a three-dimensional color representation of
a plurality of object points, the three-dimensional color
representation based at least in part on the distance to the
object, the first color value, the second color value, and the
third color value measured for each of a plurality of object
points.
12. A method for optically scanning and measuring an environment
with a laser scanner, the method comprising: providing a light
emitter, a collimator, a steering mirror rotatable about a first
axis, scanner optics, an optical receiver, a control and evaluation
unit, a color receiver, a measuring head rotatable about a second
axis, and a processor; modulating a first light; combining the
first light with a second light, a third light, and a fourth light
to obtain an emission light beam, the second, third, and fourth
lights each having a different wavelength in the visible spectrum;
collimating the emission light beam with the collimator; deflecting
the emission light beam onto an object point in the environment
with the steering mirror and in response receiving a reception
light beam reflected from the object point; receiving with the
optical receiver the reception light beam from the steering mirror;
sending with the optical receiver the first light in the reception
beam in a first path and the second, third, and fourth light in the
reception beam in a second path; receiving with the control and
evaluation unit the first light in the first path, converting the
first light into a first electrical signal, and determining a
distance to the object based at least in part on the first
electrical signal; receiving with the color receiver the second,
third, and fourth lights on the second path, converting the second,
third, and fourth lights into second, third, and fourth electrical
signals, and determining a first color value, a second color value,
and a third color value based at least in part on the second,
third, and fourth electrical signals; rotating the measuring head
around the second axis perpendicular to the first axis, the first
axis and the second axis intersecting in a gimbal point, the gimbal
point being located on the steering mirror; and determining with
the processor a three-dimensional color representation of the
object point, the three-dimensional color representation based at
least in part on the distance to the object, the first color value,
the second color value, and the third color value; and storing the
three-dimensional color representation of the object point.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation-in-Part
Application of application Ser. No. 13/259,446, which was filed
Sep. 23, 2011, which is a National Stage Application of
PCT/EP2010/001779, which was filed on Mar. 22, 2010, which claims
priority to Provisional Application No. 61/299,566, which was filed
Jan. 29, 2010, and also claims priority to German Patent
Application No. 10 2009 015 920.7, which was filed on Mar. 25,
2009, the contents of which are incorporated herein by reference in
their entireties.
BACKGROUND OF THE INVENTION
[0002] The invention relates to a device for optically scanning and
measuring an environment.
[0003] By means of a device such as is known for example from DE 20
2006 005 643, and which is designed as a laser scanner, the
environment of the laser scanner can be optically scanned and
measured. For gaining additional information, a line scan camera,
which takes RGB signals, is mounted on the laser scanner, so that
the measuring points of the scan can be completed by color
information. The camera holder is rotatable. To avoid parallax
errors, the camera, for taking its records, is swiveled onto the
vertical rotational axis of the laser scanner, and the laser
scanner is lowered until the camera has reached the horizontal
rotational axis. This method requires a high precision of the
components.
[0004] It is known to attach color cameras in or on laser scanners.
Such scanners collect color information in a series of steps
disconnected from the measuring of 3D coordinates of object points
in an environment. The color information is, a later step,
superimposed on the 3D coordinates using an interpolation and
mapping method. In many cases, color data is incomplete and, in
other cases, color data is not correctly aligned to corresponding
3D features. What is needed is a scanner having features that
overcome these limitations.
SUMMARY OF THE INVENTION
[0005] Embodiments of the present invention are based on the object
of creating an alternative to the device of the type mentioned
hereinabove.
[0006] According to an embodiment of the present invention, a laser
scanner is provided for optically scanning and measuring an
environment. The laser scanner includes a light emitter configured
to emit an emission light beam, the emission light beam being a
superposition of a first light, a second light, a third light, and
a fourth light, the first light being modulated, the second, third,
and fourth lights each having a different wavelength in the visible
spectrum; a collimator configured to collimate the emission light
beam; a steering mirror having a reflective surface and configured
to rotate about a first axis, the steering mirror further
configured to deflect the emission light beam onto an object point
in the environment and to receive a reception light beam reflected
from the object point; scanner optics configured to receive the
reception light beam from the steering mirror; an optical receiver
configured to receive the reception light beam from the steering
mirror, the optical receiver further configured to send the first
light in a first path and to send the second, third, and fourth
lights in a second path; a control and evaluation unit configured
to receive the first light in the first path, to convert the first
light into a first electrical signal, and to determine a distance
to the object based at least in part on the first electrical
signal; a color receiver configured to receive the second, third,
and fourth lights on the second path, to convert the second, third,
and fourth lights into second, third, and fourth electrical
signals, and to determine a first color value, a second color
value, and a third color value based at least in part on the
second, third, and fourth electrical signals; a measuring head
configured to rotate around a second axis perpendicular to the
first axis, the first axis and the second axis intersecting in a
gimbal point, the gimbal point being located on the steering
mirror; and a processor configured to determine a three-dimensional
color representation of the object point, the three-dimensional
color representation based at least in part on the distance to the
object, the first color value, the second color value, and the
third color value.
[0007] According to another embodiment of the present invention, a
method is provided for optically scanning and measuring an
environment with a laser scanner. The method includes providing a
light emitter, a collimator, a steering mirror, scanner optics, an
optical receiver, a control and evaluation unit, a color receiver,
a measuring head, and a processor; modulating a first light;
combining the first light with a second light, a third light, and a
fourth light to obtain an emission light beam, the second, third,
and fourth lights each having a different wavelength in the visible
spectrum; collimating the emission light beam with the collimator;
deflecting the emission light beam onto an object point in the
environment with the steering mirror and in response receiving a
reception light beam reflected from the object point; receiving
with the optical receiver the reception light beam from the
steering mirror; sending with the optical receiver the first light
in the reception beam in a first path and the second, third, and
fourth light in the reception beam in a second path; receiving with
the control and evaluation unit the first light in the first path,
converting the first light into a first electrical signal, and
determining a distance to the object based at least in part on the
first electrical signal; receiving with the color receiver the
second, third, and fourth lights on the second path, converting the
second, third, and fourth lights into second, third, and fourth
electrical signals, and determining a first color value, a second
color value, and a third color value based at least in part on the
second, third, and fourth electrical signals; rotating the
measuring head around a second axis perpendicular to the first
axis, the first axis and the second axis intersecting in a gimbal
point, the gimbal point being located on the steering mirror; and
determining with the processor a three-dimensional color
representation of the object point, the three-dimensional color
representation based at least in part on the distance to the
object, the first color value, the second color value, and the
third color value; and storing the three-dimensional color
representation of the object point.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention is explained in more detail below on the basis
of exemplary embodiments illustrated in the drawings, in which
[0009] FIG. 1 is a partial sectional view of the laser scanner
according to an embodiment;
[0010] FIG. 2 is a schematic illustration of the laser scanner
according to an embodiment;
[0011] FIG. 3 is a schematic illustration of internal components
within the laser scanner according to an embodiment;
[0012] FIG. 4 is a schematic illustration of a multi-color light
source according to an embodiment;
[0013] FIG. 5 is a schematic illustration of a color receiver
according to an embodiment; and
[0014] FIG. 6 is a block diagram illustration optional optical and
electrical elements of the color receiver.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring to FIGS. 1 and 2, a laser scanner 10 is provided
as a device for optically scanning and measuring the environment of
the laser scanner 10. The laser scanner 10 has a measuring head 12
and a base 14. The measuring head 12 is mounted on the base 14 as a
unit that can be rotated around a vertical axis. The measuring head
12 has a mirror 16, which can be rotated around a horizontal axis.
The intersection point of the two rotational axes is designated
center C10 of the laser scanner 10.
[0016] The measuring head 12 is further provided with a light
emitter 17 for emitting an emission light beam 18. The emission
light beam 18 is a superposition of three laser beams R (red), G
(green) and B (blue) which, with different wavelengths, are within
the visible range of approximately 400 to 700 nm wavelength, such
as 650 nm, 530 nm and 470 nm. The wavelengths of the three laser
beams R, G and B are selected in such a way that they define the
three-dimensional RGB color space, i.e. that they are distributed
well over the visible range. The laser emitter 17 has three laser
diodes 17R, 17G, 17B (or other lasers), each of which generates one
of the three laser beams R, G or B. The superposition can take
place by feeding the three free laser beams R, G and B into the
collimator of the light emitter 17 or by feeding them into a common
optical fiber which is then fed to the collimator.
[0017] At least one of the three laser beams R, G, B in the
emission light beam 18, and in an embodiment all three laser beams
R, G, B, are amplitude-modulated, for example with a sinusoidal or
with a rectangular-waveform modulation signal. The emission light
beam 18 is emitted by the light emitter 17 onto the mirror 16,
where it is deflected and emitted to the environment. A reception
light beam 20, which is reflected in the environment by an object O
or scattered otherwise, is captured by the mirror 16, deflected and
directed onto a light receiver 21. The direction of the emission
light beam 18 and of the reception light beam 20 results from the
angular positions of the mirror 16 and the measuring head 12, which
depend on the positions of their corresponding rotary drives which,
in turn, are registered by one angular encoder each 112, 116 (see
FIG. 1, for example). A control and evaluation unit 22 has a data
connection to the light emitter 17 and the light receiver 21 in
measuring head 12, whereby parts of such unit can be arranged also
outside the measuring head 12, for example a computer connected to
the base 14. The control and evaluation unit 22 determines, for a
multitude of measuring points X, the distance d between the laser
scanner 10 (i.e. the center C10) and the (illuminated point at)
object O, from the propagation time of emission light beam 18 and
reception light beam 20. For this purpose, the phase shift between
the two light beams 18 and 20 is determined and evaluated.
[0018] Scanning takes place along a circle by means of the
relatively quick rotation of the mirror 16. By virtue of the
relatively slow rotation of the measuring head 12 relative to the
base 14, the whole space is scanned step by step, by means of the
circles. The entity of measuring points X of such a measurement is
designated scan. For such a scan, the center C10 of the laser
scanner 10 defines the stationary reference system of the laser
scanner 10, in which the base 14 rests. Further details of the
laser scanner 10 and particularly of the design of measuring head
12 are described for example in U.S. Pat. No. 7,430,068 and DE 20
2006 005 643, the respective disclosures being incorporated by
reference.
[0019] To determine the distance d of the measuring points X by
means of evaluation of the phase shift, it is sufficient to use
only one of the three wave lengths, i.e. the modulated of the three
laser beams R, G and B. If necessary, this beam can have a somewhat
higher intensity (i.e. power of the electro-magnetic wave) compared
to the two other beams. Basically, all wavelengths are suitable to
the same extent. With regard to eye protection, which can better be
obtained with wavelengths below 400 nm, due to the behavior of the
receptors of the human eye, it is, however, advantageous to use the
blue laser beam B (with a wavelength shorter than 400 nm), for
determining the distances d of the measuring points X. If the two
other laser beams R and G are modulated as well, their evaluation
can be used for eliminating ambient light or for gaining additional
distance information.
[0020] In addition to the distance d to the center C10 of the laser
scanner 10, each measuring point X comprises color and brightness
information which is determined by the control and evaluation unit
22 as well, i.e. the brightness values for any of the three colors
of the laser beams R, G and B. Each brightness value corresponds to
a gray-tone value which is determined, for example, by integration
of the bandpass-filtered and amplified signal of the light receiver
21 over a measuring period which is attributed to the measuring
point X, namely for any of the three laser beams R, G, and B
separately. All three laser beams R, G and B consequently
contribute to gaining the color and brightness information.
[0021] Optionally, the light emitter 17 can be designed in such a
way that the three laser beams R, G and B can be switched on and
off independently of each other and that their intensity can also
be controlled. The composition of the emission light beam 18 can
then be adapted to the application. If, for example, only the
distance d and the brightness (gray-tone value) shall be measured,
it is sufficient to use, for example, the blue laser beam B and to
let the other two laser beams R and G switched off. A modular
design is also possible for the light emitter 17, so that the laser
diodes for generating the three laser beams R, G and B can be
mounted and dismounted independently of each other, for example,
being plug-in components or the like. If applicable, only the laser
diode necessary for generating the laser beam which serves to
determine the distance d, is mounted permanently.
[0022] In another embodiment described with reference to FIGS. 3-5,
the scanner 10 includes a light emitter 210 that includes a
modulated light source for measuring distance and three light beams
having R, G, and B wavelengths for producing a color image of the
environment. In an embodiment, the modulated light source that is
used to measure distance has an infrared wavelength, for example,
1550 nm or 1310 nm. The beam of light 220 emitted and collimated by
the light source 210 reflects off a stationary mirror or beam
splitter 221 before traveling along direction 230 to reflect off
rotating mirror 16 at a gimbal point 227 to travel along direction
223. The beam of light continues to object O, where it strikes the
object at a measuring point X. Light scattered or reflected off the
object returns to the rotating mirror 16, from which it enters the
scanner optics 240 in a relatively large beam of light 235. In an
embodiment, scanner optics 240 includes aspheric lens 242, mask
243, flat mirror 244, curved mirror 246, and right angle prism
reflector 248. Light passes from scanner optics into optical
receiver 250. Optical receiver may include aperture 251,
collimating lens 252A, 252B, dichroic beam splitter 254, and
fiber-optic ferrule 256. Light from scanner optics 240 passes
through the aperture 251 and is collimated by collimating lens
252A. In an embodiment, the portion of light used for distance
measurement, for example a modulated infrared portion of the light,
is passed in a first direction via a first optical path by the
dichroic beam splitter 254, while the portion of light that
includes R, G, and B wavelengths is passed in a second direction
via a second optical path into a color receiver 260. The infrared
light passes through the dichroic beam splitter 254, enters the
fiber-optic ferrule 256 and passes into control and evaluation unit
22, the control and evaluation unit including an electro-optical
receiver 270 and a processor 271, the control and evaluation unit
configured to determine the distance from the scanner to the target
point X. In an embodiment, the distance is determined by the
processor 271 based at least in part on the phases of modulated
light entering the electro-optical receiver 270. The scanner may
also include, in addition to a real-time receiver 260 (which serves
as a type of color camera), the scanner may also include a
multi-pixel color camera 280 that captures colored light passing
through a dichroic beam splitter 221. In use, the optional camera
280 captures color images at a time before or after the 3D
measurement is performed.
[0023] The color receiver 260 passes the three colors of light R,
G, B to three corresponding optical detectors 542, 544, 546 (see
FIGS. 5 and 6, for example). The light received by each of the
optical detectors is converted into an electrical signal, and
respective first, second, and third color values determined based
on the strength of the respective electrical signals from the
optical detectors, which is sent to a processor, which might be the
processor 271, another processor elsewhere in the scanner 10, or a
processor in an external computer. The three colors of light are
assigned to the corresponding distance measurement obtained from
the modulated infrared light (for example) and from angles measured
by angular encoders 112, 116, the angles indicating an angle of
rotation of mirror 16 about its axis of rotation (nominally
horizontal in the normal mounting position of the scanner 10) and
an angle of rotation of the scanner unit about a pan axis
(nominally vertical in the normal mounting position of the scanner
10, the axis passing through the gimbal point 227). In other words,
the three color values obtained from the color receiver 260 for a
given measured point X are stored by the processor 271 or another
processor along with the measured distance and measured angles for
the same measured point X.
[0024] In an embodiment, the light source 210 combines light from
four light sources 211, 213, 215, and 217 as shown in FIG. 4. One
way to combine the four wavelengths of light is to use an optical
element, such as a right angle mirror 212 combined with a
collection of serially connected dichroic beam splitters 214, 216,
and 218, for example. In an embodiment, blue light from light
source 211 is reflected by a right angle mirror 212, passes to
dichroic beam splitter 214 where it is combined with green light.
The combined blue-green light passes to dichroic beam splitter 216
where it is combined with red light. The combined blue-green-red
light passes to dichroic beam splitter 218 where it is combined
with modulated infrared light. The beam of light 220 includes all
four wavelengths provided by the light sources 211, 213, 215, and
217. In an embodiment, the blue, green and red lights are
unmodulated, while only the infrared light is modulated, for
example, by multiple different RF or microwave frequencies. In
another embodiment, illustrated in FIG. 4, the blue light source,
the green light source, and the red light source are intensity
modulated at frequencies f.sub.1, f.sub.2, and f.sub.3,
respectively, by means of electrical modulation components 232,
234, and 236. The modulation may be applied as a sine wave or a
square wave, for example. If the sample rate of the scanner is
approximately 1 MHz per second, the modulation rates might be, for
example, f.sub.1=10 MHz, f.sub.2=20 MHz, and f.sub.3=30 MHz.
[0025] In an embodiment, the color receiver 260 passes the three
colors of light to optical detectors 542, 544, and 546 as shown in
FIGS. 5 and 6. Many optical arrangements may be used to separate
the three colors of light and send these to the three optical
detectors. One method would be to use concatenated dichroic beam
splitters as was done in FIG. 4. Another way to separate the light
is to use a glass optical element, such as a trichroic beam
splitter element 520, for example. In an embodiment, light 510
reflected off dichroic beam splitter 254 contains three colors R,
G, and B. The light 510 passes into the trichroic beam splitter.
When it arrives at coated surface 522, blue light 512 is reflected
off the coating and is reflected a second time through optical
bandpass filter 547 into optical detector 546. The optical bandpass
filter may be a thin-film filter applied directly to the optical
detector 546 or it may be a separate filter element placed in front
of the optical detector. The optical bandpass filter 547 is
configured to pass blue light and to reflect or absorb other
wavelengths of light. The red-green light 514 continues to travel
in the glass until it reaches coated surface 524, where it is
separated into reflected red light 516 and transmitted green light
518. The green light 518 passes through optical bandpass filter 545
into optical detector 544. The reflected red light 516 undergoes
total internal reflection at air gap 526 before passing through
optical bandpass filter 543 into optical detector 542.
[0026] The color receiver 260 further includes electro-optical and
electrical components shown in FIG. 6. The blue light 512, red
light 516, and green light 518 reach optical detectors 546, 542,
and 544, respectively. The optical detectors convert the light
beams 512, 516, and 518 into corresponding electrical signals 605,
601, and 603. In an embodiment, the optical detectors 542, 544, and
546 are avalanche photodiodes (APDs). In an embodiment electrical
signals are sent to a transimpedance amplifier 602, 604, 606 before
being sent to a bandpass filter 612, 614, 616 and onto a high gain
amplifier 622, 624, 626. The optional bandpass filter is used if
the B, G, R light sources 211, 213, 215 are modulated at
frequencies f.sub.1,f.sub.2,f.sub.3. For example, if one million
points are measured per second, then it might be reasonable to
modulate the blue, green, and red laser diodes sinusoidal at 10
MHz, 20 MHz, and 30 MHz, respectively. In this case, the bandpass
filters 612, 614, 616 would have center frequencies of 10 MHz, 20
MHz, and 30 MHz, respectively, and each filter might have a
bandwidth of 3 MHz. Advantages of using an electrical bandpass
filter 612, 614, 616 include reduction of optical background noise
and out-of-band electrical (e.g., thermal) noise. The result is an
improvement in the signal-to-noise ratio in the desired colors
leaving the electrical bandpass filters. The electrical signals
leaving amplifiers 622, 624, 626 are sent to analog-to-digital
converter (ADC) 634, which converts the analog electrical signals
into digital electrical signals, and from which determines
respective first, second, and third color values. The digital
electrical signals are sent to a processor, which might be the
processor 271, another processor internal to the scanner 10, or a
processor in an external computer. In an embodiment, the processor
271 is configured via executable code to determine and store a
three-dimensional color representation of the object point, the
three-dimensional color representation based at least in part on
the distance to the object, the first color value, the second color
value, and the third color value. In an embodiment, the processor
271 is further configured to determine a three-dimensional color
representation of the object point based on the first angle of
rotation and the second angle of rotation. In an embodiment, the
processor 271 is further configured to determine a
three-dimensional color representation of a plurality of object
points, the three-dimensional color representation based at least
in part on the distance to the object, the first color value, the
second color value, and the third color value measured for each of
a plurality of object points.
[0027] The scanner discussed hereinabove is of a type referred to
as a time-of-flight (TOF) scanner. This type of scanner determines
distance to a target based on the time required for the light to
travel from the scanner to the target and back. This round-trip
time depends on the speed of light in air, which is equal to the
speed of light in vacuum divided by the index of refraction in air.
The index of refraction of light in air in turn depends on the
temperature, pressure, and humidity of the air and the wavelength
of the light. A scanner that operates on a different physical
principle is a triangulation scanner. Such a scanner determines
distance to a target based on a trigonometric calculation based on
triangle distances and angles. In a triangulation scanner, distance
to a target is not directly dependent on the speed of light in
air.
[0028] One type of TOF scanner modulates laser light (which might
be infrared laser light, for example) simultaneously at several
different modulation frequencies. It reflects the modulated laser
light off a spinning mirror 16 to a target. Because the light is
kept constantly moving, only a relatively small portion of the
optical power of the light has the possibility of reaching a human
eye and passing to the retina. Because of this, as long as the beam
of light is activated only when the mirror 16 is spinning, eye safe
operation (for example, class 1 laser safety operation for infrared
light or class 2 laser safety operation for visible light), with
the laser power higher than would be possible for a stationary
laser beam. For example, for laser light at 1550 nm, eye safe
(class 1) laser safety operation for a continually applied laser
beam requires that the laser power be kept below 20 mW. For 1550 nm
laser light reflected off a rapidly spinning mirror, the laser
light may be in the class 1 limit for an optical power of a few
hundred mW. A similar increase in laser power above the limit of 1
mW for class 2 (eye safe) operation for continually applied laser
light at visible wavelengths is also possible for light from laser
light sources 211, 213, and 215.
[0029] An advantage of the apparatus and methods described herein
is that colors are assigned in one-to-one correspondence to
measured 3D coordinates, thereby enabling more accurate color
matching and eliminate problems such as color skew that can occur
when mapping colors onto measured 3D points.
[0030] Although the colors in the beam of light 220 are described
above as being red, green, and blue, it is possible to use other
colors. Each set of three colors spans a color space from which
intermediate colors may be derived by combining the three colors in
various proportions. It should be understood that in the discussion
above, the three colors R, G, and B may be replaced by any other
three colors in the visible spectrum.
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